Adaptive structures are structures which can change from one stable configuration to another so as to adapt to a particular need during an operation with the structure. The structure with an ability of holding multiple configurations may have various uses in certain industries where morphing structures offer advantages. As examples, the applications include components such as valves or robotic structures as well as wings or components on aircraft or road vehicles which may be required to change in structural configuration during operation for maximum efficiencies or designed functions.
Bistable shells which can be considered to be one form of adaptive structures are manufactured with unique characteristics of having two stable configurations. They are potentially suitable for application in structures involving shape adaptation due to their unique ability to hold different stable states without any external input energy or support.
Bistable disks are the simplest bistable shells, which could be achieved without residual stresses in the initial state, such as bistable spherical rubber caps. Bistable disk are widely used in industrial and this bistable mechanism is regularly utilized to develop new functional structures, such as reconfigurable multistable shells, snap surfaces, etc. As molds in spherical configurations are used for building bistable disks, the manufacturing process is cumbersome and the configurations are not convenient to be changed.
Bistable disks with residual stresses are usually cylindrical obtained by stimulations over the structures bending in two directions, and many bistable shells are manufactured based on the same bistable mechanism, such as bistable unsymmetric composite shells obtained based on thermal effect, bistable metallic shells by plastically bending in two directions, bistable surface-stressed shells, etc. Those bistable shells are promising to be used for morphing wings. Bistable spherical disks by non-uniform growth are proposed and proved to exist theoretically. Currently there is no applicable method to manufacture bistable spherical disks using such a mechanism.
Multistable shells with an ability of holding more than two configurations are desired in the industrials for achieving a more flexible shape adaptation. Several tristable shells have been proposed and one of them was experimentally manufactured from composite shells in the art. To obtain multistable shells, multiple bistable composite shells were assembled using joints or tessellated in one structure; however, the assembled multistable structures were only results of discrete bistable shells without a smooth surface and the tessellated shells were only able to hold two stable states due to the strong coupling effect between stretching and bending deformations. Multistable dimpled or microlens based shells were manufactured but they were not suitable for bearing external loads because they were made from ultra thin shells with thickness of about 100 μm.
For current bistable disks or shells, bending deformations dominate the transitions and the load bearing capacities of the bistable disks or shells are limited. Also, the stable configurations of current bistable shells or multistable shells are limited. The manufacturing methods of bistable shells are different and thus improvements to the method of manufacturing thereof, so as to make bistable or multistable shells with designable stable configurations, may make the industrial applications of bistable or multistable shells more realizable.